The engines of heavy trucks and lorries have ranges of speeds which can be used only within very narrow limits (from 1000 to 2500 RMP), and are associated with gearboxes which have a substantial number of gear ratios, offering total reduction possibilities usually from 1 to 10. This allows using the engine correctly, the low power per unit of mass in such vehicles being taken into account.
A mistake in the ratio to be used as a function of the speed of the vehicle may result in the engine running under very abnormal and destructive conditions.
In the case of a touring car with semi-automatic control, the low number of ratios (4), the small range of reduction of the gearbox (from 1 to 4), and the very wide range of engine speeds (from 1000 to 5000 RPM) which can be used, make it unlikely for the engine to be destroyed by running under abnormal conditions as a result of a mistake in the use of the gearbox. On the other hand, when it is contemplated to go through the gears automatically on a heavy truck or lorry, safety devices against wrong handling are absolutely necessary.
The device according to the present invention aims at solving this problem by allowing the selection of the ratio of the gearbox of a vehicle, either manually or automatically.